Basil's growth, yield, and chemical composition are significantly influenced by environmental and nutritional stress.

*   **Water Stress (Drought):** Inhibits overall plant growth and significantly reduces dry herb yield.
*   **Drought Effects:** Leads to a decrease in total sugar and carotenoid concentrations.
*   **Biomass:** Drought stress reduces dry herb yield, which can be attributed to a smaller leaf area index and reduced photosynthesis.
*   **Photosynthesis:** Drought stress leads to a significant decrease in the net assimilation rate and stomatal conductance.
*   **Essential Oils:** Water stress can have a positive or negative effect on essential oil content, depending on the cultivar and stress severity.
*   **Heat Stress:** High temperatures inhibit plant growth and significantly decrease total chlorophyll levels.
*   **Oxidative Stress:** Both high temperature and water stress can cause oxidative stress, indicated by increased malondialdehyde (MDA) levels.
*   **Phenolic Compounds:** The concentration of total phenolic compounds increases in response to water and heat stress.
*   **Flavonoids:** Flavonoid content increases under high-temperature stress but may decrease under water stress.
*   **Proline and Glycine Betaine:** Under severe stress, basil plants accumulate proline and glycine betaine, which aid in cellular osmoregulation.
*   **Salt Stress:** Basil is considered moderately tolerant to salinity.
*   **Salinity Effects:** High salt levels can cause stunted growth, leaf yellowing, and reduced essential oil yield.
*   **Genotype Variation:** The response to salt stress is genotype-dependent; some cultivars may see a reduction in fresh yield while others are unaffected.
*   **Carotenoids under Salinity:** Salt stress can either increase or decrease lutein and β-carotene concentrations depending on the cultivar.
*   **Volatile Organic Compounds (VOCs):** The composition of VOCs, which contribute to the aroma, is significantly affected by salinity, with compounds like linalool being negatively impacted.
*   **Nutritional Stress:** Nitrogen content in the plant can be increased by salt stress in some cultivars.
*   **Flooding Stress:** Reduces photosynthetic rates and stomatal conductance.
*   **Combined Flooding and Drought:** This sequence of stress has a more significant negative impact on photosynthetic pigments and flavonoid content than single stress events.
*   **Pigment Reduction:** Chlorophyll a, chlorophyll b, and β-carotene levels all decrease under combined flooding and drought stress.